I am not familiar with self consolidating concrete, but a super plasticizer typically helps reduce cracking because it reduces the amount of excess water needed to place the concrete.

Are these surface cracks or are they deeper? When you say stress cracks I think of shrinkage cracks, the concrete is restrained by steel, sub-soil and other factors and as it dries and shrinks there is a great amount of stress built up and it has to shrink, so it cracks.